Field of the Invention
The present invention relates to a liquid crystal display device.
Description of the Background Art
Liquid crystal display devices, which make the best use of characteristics such as light weight, low profile, and low power consumption, are flat display devices used most frequently for portable information devices or the like represented by personal computers. A liquid crystal display panel provided in a liquid crystal display device is manufactured, for example, in a series of processes as described below.
An alignment film made of organic polymeric materials such as a polyimide is applied onto a transparent substrate in which an interconnection and an electrode forming a pixel are formed in a matrix (also referred to as an array substrate) and onto a transparent substrate in which a color filter is formed (also referred to as a color filter substrate). Subsequently, a heat treatment and an alignment treatment are performed on the alignment film to complete the alignment film.
Next, the pair of transparent substrates including the alignment film is disposed to face each other with a spacer therebetween, and a periphery of a portion between the transparent substrates is provided with a sealing agent which adheres the transparent substrates to each other. Liquid crystals fill in the space between the pair of transparent substrates adhered to each other to complete a liquid crystal display panel.
For example, a polarizing plate is adhered to an outer side of the liquid crystal display panel manufactured as described above, and a liquid crystal display device is manufactured. In the liquid crystal display device, voltage is applied between a pixel electrode and a common electrode of the liquid crystal display panel to change an alignment direction of molecules of liquid crystals. Thus, in the liquid crystal display device, transmittance of light passing through the liquid crystals is controlled, causing an image to be displayed as a result.
In a liquid crystal display device, a polarizing plate designed for a wide viewing angle may be used to improve display characteristics. For example, Japanese Patent No. 4898158 discloses the technique capable of suppressing a color shift as seen from an oblique direction by forming a polarizing plate laminated with a polarizer and a phase difference film on one of transparent substrates of a lateral electric field type liquid crystal display panel.
As the technique disclosed in Japanese Patent No. 4898158, when the polarizing plate laminated with the polarizer and the phase difference film is used as a polarizing plate on one of transparent substrates, a warp may occur due to a change in temperatures in ambient environments. In a liquid crystal display device, when a warp occurs in a liquid crystal display panel, display characteristics may deteriorate, such as occurrence of light leakage during displaying a black. The reason that a warp occurs in the liquid crystal display panel is shown in the following.
The polarizer and the phase difference film are made of resin or the like and the transparent substrates of the liquid crystal display panel are made of a glass or the like, so that there is a difference between the thermal expansion coefficient of the polarizer and the phase difference film and the thermal expansion coefficient of the transparent substrates. On the other hand, when only one of the polarizers on the pair of transparent substrates includes a polarizing plate having a phase difference film, the structure varies between the polarizing plates on the pair of transparent substrates. In other words, the thermal expansion behavior varies between the polarizing plates on the pair of transparent substrates. Thus, the force which acts on the transparent substrates caused by expansion and contraction of the polarizing plates varies between the pair of transparent substrates. As a result, a warp occurs in the liquid crystal display panel.